EC2 User Data not working via python boto command

Question

I am trying to launch an instance, have a script run the first time it launches as part of userdata. The following code was used (python boto3 library):

import boto3
ec2 = boto3.resource('ec2')
instance = ec2.create_instances(DryRun=False, ImageId='ami-abcd1234', MinCount=1, MaxCount=1, KeyName='tde', Placement={'AvailabilityZone': 'us-west-2a'}, SecurityGroupIds=['sg-abcd1234'], UserData=user_data, InstanceType='c3.xlarge', SubnetId='subnet-abcd1234')

I have been playing around with the user_data and have had no success. I have been trying to echo some string to a new file in an existing directory. Below is the latest version I attempted.

user_data = '''
    #!/bin/bash
    echo 'test' > /home/ec2/test.txt
    '''

The ami is a CentOS based private AMI. I have tested the commands locally on the server and gotten them to work. But when I put the same command on the userdata (tweaked slightly to match the userdata format), it does not work. Instance launches successfully but the file I specified is not present.

I looked at other examples (https://github.com/coresoftwaregroup/boto-examples/blob/master/32-create-instance-enhanced-with-user-data.py) and even copied their commands.

Your help is appreciated! Thanks :)

Answer 1

For User Data to be recognized as a script, the very first characters MUST be #! (at least for Linux instances).

However, your user_data variable is being defined as:

"\n    #!/bin/bash\n    echo 'test' > /home/ec2/test.txt\n    "

You should define it like this:

user_data = '''#!/bin/bash
echo 'test' > /tmp/hello'''

Which produces:

"#!/bin/bash\necho 'test' > /tmp/hello"

That works correctly.

So, here's the final product:

import boto3

ec2 = boto3.resource('ec2')

user_data = '''#!/bin/bash
echo 'test' > /tmp/hello'''

instance = ec2.create_instances(ImageId='ami-abcd1234', MinCount=1, MaxCount=1, KeyName='my-key', SecurityGroupIds=['sg-abcd1234'], UserData=user_data, InstanceType='t2.nano', SubnetId='subnet-abcd1234')

After logging in:

[ec2-user@ip-172-31-2-151 ~]$ ls /tmp
hello  hsperfdata_root